For efficient communication of information and power usage, devices in a communications system often try to operate in a synchronized manner. Synchronization between devices allows for devices to coordinate their wake up times and/or various signaling so that deices can operate in a power efficient manner and still have a good opportunity that a transmitted signal will reach an intended destination device while the device is in a state, e.g., an active or monitoring state, that it is likely to receive and recover the transmitted signal.
In order to synchronize communications, various devices in a network, e.g., WiFi devices in an 802.11 network, may rely on transmission of timing synchronization signals communicated in beacon frames as part of normal communication. In some systems, device may rely on an external timing source such as GPS satellite signals which transmit signaling outside the frequency band being used by the communications device in a network.
While devices may synchronize their internal time clocks to other devices in the same network and such device may base the network timing on an external signal such as a GPS signal received by one or more devices in the network, achieving timing synchronization between devices in a network has little impact on interference from external devices.
In the case of TDMA systems, where different devices may use communications resources at different times, TDMA resources are often allocated or used on a basis of a unit referred to as a frame. The frame duration is often set and fixed for devices in a network or system. In this manner, an based on common synchronization, device can determine when resources are to be used and/or what action is to be taken.
As the number of wireless communications devices increases, interference between devices corresponding to different networks is likely to become more common. Such interference may be from devices corresponding to a different network using the same frequency band but perhaps a different communications technology or even the same technology but a different code or other security intended to prevent communication or eavesdropping on communications. Interference may also be caused by devices using adjacent frequency bands.
Recurring interference may extend across frame boundaries in a TDMA system and may repeat as devices belonging to a different network use the same or an adjacent communications resource, e.g., frequency band. When the interference extends across frame boundaries, it can have a negative impact on two subsequent frames as opposed to be isolated to a single frame. In addition, interference mitigation techniques that may be performed on a per frame basis may be complicated since the interference may apply to limited portions of two frames as opposed to being contained within a single frame making per frame measurements and attempts at interference mitigation less successful than if the interference were contained or limited to a single frame.
In view of the above discussion it should be appreciated that there is a need for methods and/or apparatus which could be used to limit the affect of interference on frames of a communications system where the interference may be recurring or have some predictable pattern.